Magnetic random access memory (MRAM) devices use magnetic memory cells to store information. Information is stored in the magnetic memory cells as an orientation of the magnetization of a free (or switchable) layer in the magnetic memory cell as compared to an orientation of the magnetization of a fixed (or reference) layer in the magnetic memory cell. The magnetization of the free layer can be oriented either parallel or anti-parallel to the fixed layer, representing either a logic “1” or a logic “0.” When the magnetic memory cell is sitting in a zero applied magnetic field, the magnetization of the magnetic memory cell is stable. However, the application of a magnetic field can switch the magnetization of the free layer to write information to the magnetic memory cell.
Each magnetic memory cell includes at least one magnetic metal layer serving as the free layer, at least one other magnetic metal layer serving as the fixed layer, and a tunnel barrier oriented in a magnetic tunnel junction or MTJ stack. The tunnel barrier which is present between the free layer and the fixed layer, serves to decouple these magnetic metal layers while permitting electrons to pass therethrough.
In spin torque MRAM, the spin hall effect is leveraged for writing data whereby a spin-polarized current is passed through a spin hall wire which destabilizes the free layer in the MTJs along the spin hall wire, making them easier to write. A problem with this design, however, is that the spin hall wire has a high resistivity, thereby limiting the number of bits that can be placed on the same wire.
Therefore, improved spin torque MRAM designs would be desirable.